dip only understands a predefined set of variables. A variable name always begins with a dollar symbol and must be written in lower-case letters.
The $local and $locip variables contain the local host's name and IP address. Setting the hostname makes dip store the canonical hostname in $local, at the same time assigning $locip the corresponding IP address. The analogous thing happens when setting the $locip.
The $remote and $rmtip variables do the same for the remote host's name and address. $mtu contains the MTU value for the connection.
These five variables are the only ones that may be assigned values directly using the get command. A host of other variables can only be set through corresponding commands, but may be used print statements; these are $modem, $port, and $speed.
$errlvl is the variable through which you can access the result of the last command executed. An error level of 0 indicates success, while a non-zero value denotes an error.